Master cylinder - The 1947 - Present Chevrolet & GMC Truck Message Board Network

CURSED GEARS · 04-26-2013, 04:46 AM

Greetings gang.

First off, let me say I have a 70 Chevy long bed truck. I tell you this so you dont think I'm just here fishing for advise on a non related project. Now for the problem.
I've pretty much just finished a 7 year project on a 39 Chevy truck. Its a hot rod, and has several parts from different manufactures, (chevy Ford, Dodge) Anyway, during brake design, another site I'm a member of reccomended the 67-72 Chevy master cylinder for my project. I guess the bore size is correct for the wheel cylinders I've used. Anyway, I can't seem to get any real pressures to the wheels. The pedals not hard. I push the brake pedal down and dont really get brake until near the end of the pedal.
The master cylinder was bled, and the rest of the system was bled several times. The shoes have been adjusted until they drag on the drums. I have drums front and back, and the master cylinder is drum/drum.
My question to you guys is, for you guys who are running drum/drum brakes, do you run a residual valve? I've cracked open my rear bleeder screw, and nothing leaks out. There is no pressure on it at rest. I'm wondering if a residual valve would help.
Second question is, Are the chambers on the master cylinder specific? That is to say, is the front chamber for the front, and the back chamber for the rear? Does it make a difference?
I know theres a lot of sharp guys on here, I've been on this site for years, and I would appriciate any advice you might have to give.

Thanks,
Cursed Gears.

Tx Firefighter · 04-26-2013, 07:35 AM

Is your master cylinder under your floor or on the firewall ?

If its under the floor, you will need residual valves. That would explain why you aren't getting fluid flowing out of the bleeders by gravity alone. The master cylinder isn't high enough above the wheels for our old friend gravity to do the work.
Posted via Mobile Device

crawdadfox · 04-26-2013, 07:41 AM

Did you bench bleed the cylinder?

CURSED GEARS · 04-26-2013, 11:05 AM

Guess I left some info out. The master cylinder is on the firewall, and yes, I did bench bleed the master cylinder.
I did just read up on mastercylinders, and I guess they primairy and secondary pistons. If I read right, the back chamber is for the rear, and operates first, as you continue to push, the fronts starts to come on. Thats problem number one I will have to fix, right now, the front chamber of my mastercyliinder goes to my back brakes.
Thanks for replying guys. Still interested in your opinion of a residual valve.

04-26-2013, 04:46 AM	#1
CURSED GEARS Registered User Join Date: Aug 2010 Location: Lafayette In. Posts: 252	Master cylinder Greetings gang. First off, let me say I have a 70 Chevy long bed truck. I tell you this so you dont think I'm just here fishing for advise on a non related project. Now for the problem. I've pretty much just finished a 7 year project on a 39 Chevy truck. Its a hot rod, and has several parts from different manufactures, (chevy Ford, Dodge) Anyway, during brake design, another site I'm a member of reccomended the 67-72 Chevy master cylinder for my project. I guess the bore size is correct for the wheel cylinders I've used. Anyway, I can't seem to get any real pressures to the wheels. The pedals not hard. I push the brake pedal down and dont really get brake until near the end of the pedal. The master cylinder was bled, and the rest of the system was bled several times. The shoes have been adjusted until they drag on the drums. I have drums front and back, and the master cylinder is drum/drum. My question to you guys is, for you guys who are running drum/drum brakes, do you run a residual valve? I've cracked open my rear bleeder screw, and nothing leaks out. There is no pressure on it at rest. I'm wondering if a residual valve would help. Second question is, Are the chambers on the master cylinder specific? That is to say, is the front chamber for the front, and the back chamber for the rear? Does it make a difference? I know theres a lot of sharp guys on here, I've been on this site for years, and I would appriciate any advice you might have to give. Thanks, Cursed Gears.

04-26-2013, 07:35 AM	#2
Tx Firefighter Watch out for your cornhole ! Join Date: Jun 2003 Location: Azle, Texas Posts: 14,162	Re: Master cylinder Is your master cylinder under your floor or on the firewall ? If its under the floor, you will need residual valves. That would explain why you aren't getting fluid flowing out of the bleeders by gravity alone. The master cylinder isn't high enough above the wheels for our old friend gravity to do the work. Posted via Mobile Device

04-26-2013, 07:41 AM	#3
crawdadfox Registered User Join Date: Aug 2008 Location: New Orleans Louisiana.....a great place to visit but you wouldn't want to live here!!! Posts: 883	Re: Master cylinder Did you bench bleed the cylinder? __________________ Down......with the sickness!!

04-26-2013, 11:05 AM	#4
CURSED GEARS Registered User Join Date: Aug 2010 Location: Lafayette In. Posts: 252	Re: Master cylinder Guess I left some info out. The master cylinder is on the firewall, and yes, I did bench bleed the master cylinder. I did just read up on mastercylinders, and I guess they primairy and secondary pistons. If I read right, the back chamber is for the rear, and operates first, as you continue to push, the fronts starts to come on. Thats problem number one I will have to fix, right now, the front chamber of my mastercyliinder goes to my back brakes. Thanks for replying guys. Still interested in your opinion of a residual valve.



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